Heat treatment apparatus



Aug. 20, 1968 P, Boc ETAL 3,398,252

HEAT TREATMENT APPARATUS Filed Nov. 15, 1965 2 Sheets-Sheet 1 250 v THREE PHASE W T FIG I 4 8 2 6 HEATING COIL POWER CONTROL RECTIFIER OSCILLATOR MEANS 2 PHOTOsCANNER TRANSFORMER RECTIFIER OSCILLATOR SATURABLE REACTOR REGULATOR 35 THREE PHASE I POWER 45 39 GUAGE COMPUTER WIDTH MEANS -47 ALLOY f (3 )(4l)(43)(47) REQUIRMENT WITNESSES:

INVENTOR 5 3/ Ashley P. Bock, Frank E. Henry gvflw W and John A. Redmond ATTORNEY Aug. 20, 1968 Filed Nov. 15, 1965 A. P. BOCK ET AL 3,398,252

HEAT TREATMENT APPARATUS 2 Sheets-Sheet 2 29 24v GAUGE WIDTH ALLOY REQUIRMENT ,J

H BIAS DIODE FUNCTION NETWORK (D O (I J aw I 53 &

SATURABLE REACTOR To TRINISTOR (CONTROLS FIRING SATURABLE ANGLE 0|: F-,9; 'l REGULATOR TRINISTOR REGULATOR) AC POWER m F IG. 3.

O X A o 590- 2 g KILOVOLTS lo 3 g g FIG. 2. J E Z LU E g 550- p. j g TEMPERATURE 6 w AND g 53o KILOWATTS t X LU slo l l l l l I l l l 400 soo 800 I000 I200 I400 I600 I800 LINE SPEED United States Patent 3,398,252 HEAT TREATMENT APPARATUS Ashley P. Bock, Baltimore, and Frank E. Henry and John A. Redmond, Ellicott City, Md., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., 21 corporation of Pennsylvania Filed Nov. '15, 1965, Ser. No. 507,932 2 Claims. (Cl. 219-10.61)

ABSTRACT OF THE DISCLOSURE An apparatus for continuous heating of longitudinallyadvancing tin plated steel strip entering a quenching station to' obtain alloying of the tin with the steel. A first heating and control means heats the strip to obtain melting of the tin along a flow-line automatically held at a fixed location along the heating line irrespective of strip speed, and a second heating and control means heats the strip further to raise the strip temperature with a high degree of accuracy to different speed-determined values by automatic regulation in reliance on the stable reference point conditions existing in the strip at the fixed site of the flow line.

It has been proposed to heat tin plated steel strip to a temperature above the melting point of the tin plating on the surface of such strip followed by quenching in a liquid bath to obtain alloying of the tin with the steel for purposes of improving the protection afforded by the tin to the steel.

It is desirable that the apparatus for performing such heating of tin plated steel strip material be operated in a continuous manner successively through a heating station and a quenching station. It is also desirable that the rate of travel of the steel strip during such heat treatment be at a relatively high production rate, and that the temperature to which the strip is heated prior to introduction to the quenching bath be accurately regulated, preferably within plus or minus five degrees F. Accordingly, it becomes an object of the present invention to provide heat treatment apparatus which is capable of obtaining such desired result.

It also is desirable to be able to regulate the producferent lengths of time enroute to the quench bath. To'

obtain a particular desired alloying condition of the strip under such variable time-at-temperature conditions it becomes necessary to vary the temperature to which the strip is heated prior to entiy into such bath according to the rate of strip speed. It thus becomes another object of the present invention to provide a heat treatment apparatus for alloying of tin plated steel strip by continuous heating and quenching in a fixed travel distance quench bath, which apparatus automatically regulates the temperature to which the strip is heated according to the speed of travel of the strip through the line commensurate with the desired alloying condition corresponding to such strip speed.

In general, the present invention satisfies the above 3,398,252 Patented Aug. 20, 1968 objects by provision of an induction heating coil means through which the strip passes to obtain such rapid heating thereof as to realize melting of the tin plating on the surface of the strip along a flow line extending transversely of the strip and within the domain of such heating coil means; to observe such flow line with a photoscanner means and providing a heating coil power control means responsive to information from such photoscanner means to so regulate the output of the induction heating coil means as to obtain a fixed position of such flow line with respect to such heating coil; and to provide a second heating source and control means, separately regulatable with respect to the first heat source, including control means responsive to speed of travel of the strip to automatically regulate the effectiveness of such second control means to obtain the desired heated strip temperature automatically with the required degree of accuracy irre-.

spective of the speed of travel of such strip. By virtue of such arrangement where the strip is heated initially to a certain fixed temperature as represented by the melting of the tin on the surface of the strip at a certain location as determined by a fixed position of the flow line observed by the photoscanner affiliated with the first heating means, such uncontrollable variables as moisture variations on the surface of the strip are eliminated for the strip as it appears to the second heating means for its final stage of heating and the function of the control means afiiliated with the second heating meanscan be performed with a degree of certainty and accuracy based merely on known performance capability of the second heating means in response to different energy level inputs at different strip speeds and strip temperature desired to be obtained at such speed.

In accord with an alternate construction of the apparatus, the control system afliliated with the second heating means can be made to function to automatically adjust set point temperature for operation of the heating means according to line speed information, and to check the actual strip temperature obtained thereby by suitable temperature sensing means to produce an error signal to which the control means will respond to any Vernier adjustments in heat applied to the strip.

Other features, objects, and advantages of the invention will become apparent from the following more detailed description of the invention when taken in connection with the accompanying drawings, in which:

FIGURE 1 is a block diagram of the heat treatment apparatus of the present invention;

FIG. 2 are curves showing operating relationships obtained by the apparatus of FIG. 1; and

FIG. 3 is a schematic representation, partially in block diagram form, showing an illustrative form of computer embodied in the apparatus of FIG. 1.

Referring to FIG. 1, the tin plated steel strip 10, which may vary in thickness from about 4 to 15 mils and in width from 30 to 40 inches, is in continuous form and is advanced longitudinally by roller means (not shown) to pass consecutively through a first heating means in the form of an induction heating coil means 12 and a second heating means preferably in the form of second induction heating coil means 11 and thence to a quench bath 15. The function of the first induction coil means 12 is to heat the strip 10 up to a temperature at which the coating of tin on the surface of the strip begins to melt, namely 452 F., at some longitudinal fixed location along the length of such coil and subsequently heat the surface of such strip to a final alloying temperature of from 500 to 650 F., for example, according to travel speed of the strip, prior to introduction to the quench bath 15. The length of the heating coil 12 is relatively short, having perhaps ten turns and being about two to four feet long, the heating capability of the coil 12 is applied to such high concentration that the tin coating on the surface of the strip is made to melt along a sharp flow line (not shown) which is observable by a photoscanner 68 and has a sharp line of demarcation between the melted and unmelted tin which runs across the width of the strip. The temperature to which the strip including its tin coating is finally heated by the second coil means 13 for purposes of alloying or fusing such tin coating to a desired degree with the steel material of which the strip is composed, is determined according to a time-temperature function. It varies according to the time at which the strip remains at a certain heated temperature and the degree of such temperature. Curve 17 in FIG. 2 shows a typical relationship which may exist between the ultimate temperature to which the strip 10 is heated and the speed of travel of the strip, or line speed, for obtaining proper final alloying conditions of the strip after leaving the quench bath 15.

The tin plated strip 10 prior to introduction to the first heating coil means 12, may have been subject to variant degrees of preheating from previous operations performed on the strip, its surface may have more or less amounts of moisture on it, etc.; but by suitable control of the power applied to the heating coil means 12 and as affected by a suitable control means atliliated therewith, the strip 10 in being heated up to its tin melting temperature at a precise location within the coil means 12 along the heating line establishes an accurate reference point from which can readily be determined the amount of heat which must be provided by the second coil means 13 to raise the strip up to its final temperature. As presented to the coil means 13, the strip is always introduced at the same temperature and without surface moisture which will have been evaporated by virtue of having been heated to such melting temperature. Thus, it will be appreciated that the strip 10 as heated by the coil means 12 up to the tin melting temperature is presented to the second coil means 13 in a condition which eliminates nonmeasurable heat-demand-varying conditions.

To effect and control energization of the first heating coil means 12 to obtain a stabilized fixed-position flow line heated condition of the strip 10 at a particular location in the heating coil means 12, there may be provided a system such as shown, for example, in United States Patent 2,813,186, issued to A. P. Bock, Nov. 12, 1957. Portions of the apparatus of FIG. 2 in such patent have been shown in FIG. 1 of the present drawings in affiliation with the coil 12. Wherein the present showing is a duplication of the showing in such FIG. 2 of Patent 2,813,186, the same reference numerals have been applied. Such apparatus comprises an oscillator 26, which, for example, may generate a frequency of 100 kc., with its output leads connected in series with the induction coil means 12. The oscillator 26 is availed of a direct current supply from a rectifier means 48 the input to which is regulated, hence output from the oscillator 26 is regulated, by a heating coil power control means 19, which has been shown in block diagram form, but the details of which may take the form as shown in FIG. 2 of the aforementioned patent. Such apparatus functions responsively to information obtained from a tachometer generator 76 responsive to speed or travel of the strip 10 and to slight variations in flow line position obtained by the photoscanner 68 to so regulate the power applied to the induction coil means 12 as to obtain the desired result of so heating the strip 10 as to obtain the previously discussed stabilized fiow line temperature condition. The photoscanner 68 will observe such flow line at a point within and near the exit end of the coil 12 in order to allow for some slight variation in the flow line position,

and the strip 10 will leave the coil means 12 at some stabilized temperature slightly higher than the flow line temperature of 452 R, such as 465 F., for example.

The means for obtaining regulation of the power applied to the second heating coil means 13 to obtain the desired final strip temperature preparatory to introduction to the quench bath 15, as illustrated by way of example herein, comprises an oscillator 21 having its output in series with the heating coil means 13 and which is availed of a regulated direct current supply from a rectifier means 23 which is availed of regulated three-phase alternating current by way of a transformer means 25, which in turn is availed of regulated alternating current in its primary by a saturable reactor means 27. Control of regulated ouput from the saturable reactor means 27 in turn is controlled by a computer means 29 through the medium of a regulator means 31 and leads 33 and 35 from such regulator via which the direct current control signal to the saturable reactor means 27 is conducted. Since the heating demand of the coil means 13 will be imposed on the strip 10, it is a function of the thickness of such strip, the width of such strip, and the desired strip temperature which in turn is a function of the travel or speed of the strip. Such operating parameters as gauge, width, and alloy requirement are introduced as manually adjustable inputs as indicated by arrows 39, 41, and 43, respectively. Information as to strip speed is fed to the computer means 29 for automaticadjustment in response thereto from a tachometer generator 45 by way of output leads 47 therefrom.

The computer means 29 can be of a relatively simple analog form which accepts information as to gauge, width, alloy requirement, and speed in the form of direct current voltage levels to produce the desired power demand signals according to the strip temperature desired. This, can take the form of an exciter generator similar to that employed in the apparatus disclosed in the Bock Patent 2,813,186 having a plurality of field windings respective to the operating parameter information together with a suitable function generator to convert the speed signal information into proper form for correlation between line speed heat output from the coil, and the alloying temperature required. Alternatively, the computer 29 may simply take the form as shown in FIG. 3, employing a saturable reactor assembly in lieu of the exciter generator and employing a function generator which comprises a parallel arrangement of adjustable resistors respective to the three variable inputs 39, 41 and 43 of strip gauge, strip width, and alloy requirement feeding a DC control signal via leads 46 and 49 to a control winding (not shown) of a saturable reactor 51 to control the firing angle of a trinistor regulator, both of which can constitute parts of the regulator 31. The output from the tachometer generator 45 is suitably modified by a bias diode function network 53 to feed a suitable DC signal via leads 55 and 57 to another control winding (not shown) of saturable reactor 51 for effecting proper influence of the strip speed to produce a power input to the strip which obtains the relationship exemplified by curve 17 in FIG. 2.

While the invention has been described herein with respect to an exemplified embodiment of such invention, it will be appreciated that modifications may be made without departing from the true spirit and scope of the invention as intended to be defined by the appended claims.

What we claim as our invention is:

1. An apparatus for the continuous heating of tin plated steel strip while being advanced longitudinally through a heating line to a quenching medium, said apparatus comprising a first induction heating and control means for applying heat to such strip in a manner which obtains melting of the tin on the surface thereof along a clearly distinguishable flow line extending across the width of such strip and automatically maintained at a substantial fixed location along such heating line irrespective of strip advancement speed, and second induction heating and control means including strip speed sensing means to further raise the temperature of such strip to different values dependent on strip speed under automatic regulation in reliance upon the stable reference point conditions existing in the strip at such fixed flow line location.

2. The apparatus of claim 1, wherein the first induction heating and control means includes a photoscanner in observance of the aforesaid flow line, and the second induction heating and control means includes a com- UNITED STATES PATENTS 1,646,498 10/ 1927 Seede 219--10.71 X 2,669,647 2/ 1954 Segsworth 219-10.71 2,813,186 11/1957 Bock 219-l0.61

RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner. 

